This invention relates to a process for the preparation of various acetoxyacetophenones. More particularly the invention relates to the conversion of phenyl acetate to acetoxyacetophenones by a palladium catalyst in the presence of oxygen, acetic anhydride and acetic acid at elevated temperatures and pressures. The presence of a metal acetate or a mineral acid, in addition to the aforementioned materials, can influence the product distribution. Acetoxyacetophenones are used in pharmaceutical formulations. Preparation of phenyl acetate is disclosed in U.S. Pat. No. 4,156,783.
In Preparative Organic Chemistry, edited by G. Hilgetag and A. Martini, John Wiley & Sons, 1972, pages 934-935, it is disclosed that acetylation of aromatic compounds containing electron-donating substituents, and phenyl acetate is such an aromatic compound, give ortho- and para-compounds almost exclusively. Thus it is surprising that applicants' method can result in favoring meta isomers.
The acetoxylation of acetophenone using Pd(II) and potassium peroxydisulfate yields acetoxy derivatives having an isomer distribution of 1% ortho, 77% meta, and 22% para according to Acta Chemica Scandinavia B30 (1976) 361-364, Eberson et al.